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We thank Dr Hardell for his comment1 on our article concerning analyses regarding head position of mobile phone use.2

In our analysis on ipsilateral use, we included cases who used their mobile phone on the same side as the tumour or on both sides of the head, cases who were not regular users (the reference category) and all their matched controls. In our analysis on contralateral use, we used cases who used their mobile phone on the opposite side as the tumour, cases who were not regular users (the reference category), and all their matched controls. The reference category was thus made by the same participants in the two separate analyses. These two separate analyses are thus not really ‘stratified’ analyses since the two subsamples are not disjoint.

We chose this strategy because it seemed to us more natural and appropriate to keep matched sets to compare cases to their controls rather than to artificially assign a ‘tumour side’ to the controls as in Interphone3 and Hardell et al’s studies,4,5 which leads to the exclusion of a large number of participants.

However, as requested by Dr Hardell, table 1 presents results of the laterality analysis using Interphone’s method,3 for the main indicator (cumulative duration of use). As with our method, the results give higher OR for ipsilateral use (OR=4.21, 95% CI 0.70 to 25.52 for gliomas) compared with contralateral use (OR=1.61, 95% CI 0.36 to 7.14), without significant association. Moreover, as with our method, the two estimates of the ‘stratified’ OR are not grouped around the ‘total’ estimated OR for meningiomas. Such a result was also observed in a recent publication by Hardell et al5 (in table 4). All these results suggest higher ORs for heavy ipsilateral use than for heavy contralateral use, however, they are not all statistically significant. Furthermore, when using cases only as in Inskip et al’s6 study, we found a significant association between the side of phone use and the side of the tumour for glioma (OR=2.40, 95% CI 1.002 to 5.73) but not for meningiomas (OR=0.77, 95% CI 0.26 to 2.22).

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